Urgyen Chodron wrote:when you go to a website on kalachakra and the lineage i was in and see that they talk about seminal retention in the empowerments, there is nothing else to talk about. put it together with what i read in the book, it is easy to even accept the trimondis. i do not believe that buddha ever taught the tantras and many scholars agree that he didn't. it basically came from india, and even a lot of hindus are against it, embarrassed by it and call it black magic. don't ask me where i read this because i don't wish to look for the sources again.
The tradition is that Buddha Shakyamuni transformed into Heruka to subjugate the most powerful samsaric deities, and in that form while simultaneously in his human form, transmitted the practices of initiation, mandala, deity yoga and completion stage to different kings and such so they could have a road to buddhahood in one life. The Guhyasamaja, Kalachakra, Hevajra, Chakrasamvara, etc., etc., are all like this. The particular places and times of these transmissions is known in the traditions. There are others Guru Rinpoche transmitted when he met Vajrasattva and Vajrakilaya has him as the Buddha transformed. The Dzogchen Tantras come directly from Samantabhadra. Some Mahasiddhas like Saraha and Tilopa achieved levels in Tantric practice and had direct contact with Buddha Vajradhara and some Mahamudra Dakini tantras were revealed. The early tantras were not written until much later than their transmission. They were kept in an oral lineage of utter secrecy for 1000 years or so before different masters started writing them down.
So you need to understand this history. You also need to understand there are different levels of tantras, and then the oral lineages that stem from those tantras can vary dramatically from what the tantras say. In Kagyu, which has two main tantras in the tradition, Chakrasamvara and Vajradakini, the practice is deity yoga, and Six Yogas of Naropa. There's no karmamudra in Six Yogas. But you won't know that from reading the Chakrasamvara Tantra which talks about karmamudra throughout.
Tantra is a big world. Explore it with an open mind before deciding to discard it. There are many things here that really do accelerate the awakening process, particularly with respect to prana, nadi and bindu. These are real, related to the physical functions of the body-mind complex. There are very high level practices that do not involve sex, like Avalokiteshvara rituals, Green Tara, etc. But the groundwork for all these vajrayana practices comes from these tantras that do involve working with sexual energy. Keep in mind, that we are all Earth, Fire, Water, Wind and Space. Sexual energy is nothing more than that.
Finally, tantra is also intended to cause you to overcome your conceptual predilections. It introduces many taboos to your practice so that you can let go of your ego attachments. Nothing like screwing your mother in a cremation ground covered in corpse ash and human skins whilst blowing on a human femur trumpet while eating shit, spit, snot, semen and menstrual blood to burn up your conceptual mind. Of course, I'm talking about a visualization....